Thermal protective device for electric circuits



Aug. 25, 1942. E. H. TAYLOR 2,293,953

THERMAL PROTECTIVE DEVICE FOPKELECTRIC CIRCUITS Filed Sept. 28, 1938 Patentcd Aug. 25, 1942 THERMAL PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS n Eimer H. Taylor, Newburyport, Mass., assigner-to The Chase-Shawmut Company, Newburyport, Mass., a corporation of Massachusetts Application September 28, 1938, Serial No. 232,163

35 Claims. (Cl. 20o-123) This invention .relates to electric circuit interrupters and to thermal or fusible protective devices of the type wherein a movable circuit controlling or interrupting element is held in circuit closed position by means including a mass of readily fusible material which is adapted to be heated by current traversing the device to fuse orrelease its hold on the circuit controlling member and effect its movement into a circuit interrupting/position, th character and arrangement of the parts being such as, or heat absorbing means being employed, to delay the fusing ofthe readily fusible material for a satisfactory period of time following the initiation of a modcrate overload current so that the device. will not open the circuit unnecessarily when traversed by moderate overloads of short duration which the circuit conductors and the apparatus therein can withstand safely.

With such a device there is sometimes associated a fusible link that is adapted to blow promptly when traversed by heavy overloads to interrupt the circuit.

One of the objects of the present invention is the provision of an improved and simplified form of fusible protective device of the order above described and particularly one wherein the fusible element or link also constitutes the heating means for the readily fusible material.

Another object of the invention is the provision of a fusible circuit interrupter having its parts contained within and carried by a tubular enclosing casing of the cartridge fuse type.

A further object of the invention is the provision in a fusible circuit interrupter of a novel arrangement of heat absorbing member; also its relation and cooperation with the cartridge fuse type of casing. l'

A yet further object of the invention is a fusible protective device wherein the heat ab sorbing member forms a` partition of the enclosing casing and whichmember separates the fuse link compartment from the delayed circuit opening compartment and which, as one advantage, permits the fusible link to be surrounded by an arc quenching medium or filler, while keeping the other compartment free from the filler. It is also an object of the invention to provide a thermal protective device of the type described wherein spring means is employed to open the circuit upon moderate sustained overload and wherein the fusible link, and also preferably the major part of the circuit interrupting member is free from spring-applied stress.

'Applicant has found-that quartz sand is an 55 excellent iiller for short circuit current operation as it quickly extinguishes a heavy arc without l permitting the creation of an elevated internal gas or vapor pressure that is liable to rupture the casing. Applicant has found, however, that quartz sand is liable to have a temperature-conduction effect. That is to say, when the sand is subjected to a heavy arc, although the arc is extinguished quickly, the sand may be suiliciently heated to become a partial conductor and, if potential is maintained on the terminals of the fuse for a sumcient time following the blowing of the fusible link, some current passes through the heated strata of the sand and maintains itself or the current may even increase, the temperature of the sand also rising due to its decreasing resistance which allows the passage of an increasing current. Thus a hazardous condition is created.

It is an object of the present invention to provide means associated with a fuse having a filler liable to give a temperature-conduction effect, the means being responsive to heat generated by said effect to secure the positive interruption of the circuit.

It is a further object of the invention to provide a protective device including a fusible link surrounded by a filler and a fusible circuit interrupting device, the circuit interrupting device receiving heat due to the temperature-conduction effect of the filler and being in series with the fuse and the filler to effect the interruption. of the circuit.'

A yet further object of the invention is generally to improve the construction and operation of fusible protectivev devices.

Fig. 1 is a side elevation of a fusible protective device embodying the present invention.

Fig. 2 is a longitudinal section taken through the longitudinal axis of the device of Fig. 1.

Fig. 3 is a longitudinal section taken at right angles to Fig. 2 or along line 3--3 of Fig. 2.

Fig. 4 is a section taken along line 4 4 of Fig. 2.

Fig.` 5 is a perspective view of the movable flexible circuit interrupting element of Figs. 2 and 3.

Fig. 6 is a perspective view of a modified form of circuit interrupting element. Y

Fig. '7 is a view similar to Fig. 3 but illustrating the relation of the parts when the circuit is interrupted by the blowing of the fusible link.

Fig. 8 is a view similar to Fig. 7 but showing the circuit open position of the movable circuit controlling member caused by a temperaturelany suitable manner.

The casing is provided with an annular inset groove it intermediate its ends and preferably somewhat nearer the left hand end than the right hand end Said groove may be formed by rolling or other suitable operation and proV vides the interior of the tube with an inwardly directed annular ange i3.

A heat absorbing member 2Q comprising a thick metal disc or cylinder of a metal having good heat absorbing ability such, for instance, as copper, and a diameter which nts freely yet without undue looseness Within the` tubular casing is seated upon the flange it and forms a partition wall which isolates the tube compartments on opposite sides of it. The character and mass of the member largely govern the period of delay of operation of the device upon moderate overloads. A exible conductor 22 preferably of copper or other material of high electrical conductivity and of such dimensions as to oder low resistance and heating comprises a movable circuit interrupting element or member of the device and is located within the right hand compartment of the casing and is electrically connected permanently with the end cap it and removably with the heat absorbing member 2li. For this purpose the outer end part of the conductor is provided with an extension 2d of reduced width which is extended through the perforation 25 formed in the bottom wall of the depression 2S in the end wall of the end cap itl and is soldered permanently thereto by a mass 2B of relatively high melting temperature solder althoughv other suitable securing means may be employed. The other end of the iiexible conductor is provided with a reduced extension 30 which is folded upon itself to provide a doubled projecting part Sli and a spring attaching part 36 that overlies the broad face of the conductor. The doubled part of the extension is located in an axial hole 38 extended through the heat absorbing member 20 and is removably retained therein by a mass @El of relatively loW melting point material as solder which solder may more or less completely fill the hole 38.

A tensile spring 42 has one end 4t hooked into a, perforation 56 of the extension part 36 of the conductor. The other end of the spring is provided with a hook t8 which is hooked over the end of the casing l under the end cap I4. ThusV the spring exerts a constant tension on that end of the conductor retained by the low melting point solder in the hole of the heat absorbing member 20. When said solder is heated to the fusing point or sumciently to releaseits hold on the conductor the spring action causes the conductor to be withdrawn out of the hole and away from the heat absorbing member into some position as illustrated in Fig. 8, thereby interrupting the circuit through the device. The conductor 22 is flexible for this purpose.

A modified form of conductor and circuit interrupting member is illustrated in Fig. 6. In this figure the conductor 22a is vcomposed of a plurality of laminations herein illustrated as three laminations, 50 which are free from each other except at their ends where they are intended to be soldered at one end to the end cap it and at the other end to the heat absorbing member as with the conductor 22. The conductor 22a near the heat absorbing member is provided with a struck out loop part b2 over which the end of the spring 2a is adapted to be hooked to Withdraw the conductor from the heat absorbing member to effect circ'it interruption when the low melting point solder is fused. This type of conductor is adapted to carry a relatively heavy current without undue heating and yet by its laminated construction is flexible and can be exed by the spring to i effect circuit interruption upon the fusing of the low melting point solder.

Associated' with the parts above described is a fusible link 5ft which also constitutes a heater for the fusible metal d6. Said fusible link is convenientiy in the form of a straight 'flat ribbon and has one end extended through the bottom of the cup 55 of the end cap yl2 and soldered therein with relatively high melting point solder. The other end of the fuse link is extended through the hole 38 in the heat absorbing member 2t and has a reilexed end 58 that is bent over upon the right hand face of the member and is electrically and thermally' connected thereto and to the circuit interrupting member 22 by the low melting point solder liti. Thus the fusible link is in good heat conducting relation wth the heat absorbing member. The fusible link preferably is provided with an intermediate portion of reduced cross-sectional area as by the perforation t@ therein which defines the region of fusion of the link.

The link is so arranged that it will not blow at currents which ultimately cause the fusion of the low melting temperature solder and the release of the circuit interrupting member 22. The fuse link, however, is designed to blow promptly on heavier currents approaching short-circuit value and before the low melting temperature solder can release its hold on the circuit interrupting member 22. The fusible protective device thus provides delayed interruption of the circuit on moderate overloads and prompt interruption of the circuit on heavier overloads.

The fusible link 54 for carrying continuously current of about 30 amperes and upwards can be made conveniently of copper. It is, however, smaller in cross section, or consumes more power, than the conductor 22, which also'is of copper, so that it generates suicient heat to fuse the low melting temperature solder on moderate overloads without the link of itself fusing. For low continuous currents, say below 30 amperes, the fuse link preferably is made of some material having a higher electrical resistance than copper as, for instance, a copper-nickel alloy so that it will generate sufficient heat when traversed by a moderate overload current to fuse the low melting point material 48 and effect the operation of the circuit interrupting member 22. The heat generated in the fusible link is absorbed by the heat absorbing member 20 so that said member and the low melting point material 40 become elevated in temperature substantially together. While the low melting point material is here shown as completely filling the hole 38 in the heat absorbing member in practice it may not completely ll the hole. This is of no particular importance so long as sufficient low melting point is imbedded withparticles of an arc from the left hand end until the heat absorbing member seats on the flange I8. The spring is then hooked onto the other end of the casing and the reduced end 24 ofthe circuit interrupting cap l2 isapplied thereon, the end of the fuse link being threaded through the hole in the end spring carries no current injurious to it and, if tne circuit interrupting member 22 should happen to fuse the spring 42 would also fuse thereby interrupting the circuit.

The filler material 62 surrounding the fusible link preferably is a quartz sand. Applicant has :found that quartz sand is particularly eiective in extinguishing the circuit interrupting are tential on and a current flow through the circuit.

The present construction prevents a serious increase in the temperature-conduction elect and utilizes such eiect to open the circuit by the circuit interrupting member 22. That is to say.

' filler are heated sumit has been calibrated.

I claim:

1. In a thermal circuit a flexible conductor, a, readily fusible material for withdrawing said circuit interrupting conduc-` tor in response to the fusing of said material.

4. In a thermal circuit protector, a block having a hole through it, a heating conductor having one end in said hole, a circuit interrupting conductor having one end in said hole, a readily fusible material Joining the ends of said conductors, and means for withdrawing said circuit interrupting conductor in response to the fusing of said material, said heating conductor also constituting a fusible link.

5. In a thermal circuit protector, a heat absorbent block'having a hole through it, a heating conductor having one end inserted in one direction in said hole, a flexible conductor having one end inserted in the opposite direction in said hole, a readily fusible material in said hole connecting said conductors and receiving heat from said heating conductor and adapted to fuse' and release its hold from said flexible conductor, and means. responsive to the fusing of said fusible material for withdrawing said flexible conductor from said hole, said block having a large heat absorbing capacity as compared with the fusible material, and said heating conductor being fusible and arranged to fuse at a higher current maintained for a shorter period of time than will fuse said readily fusible materiah 6. In a thermal circuit protector, a heat absorbing block, a fusible heating conductor having one end thermally connected with said block, a circuit interrupting conductor electrically connected in series relation with said heating conductor and thermally connected With said block by a mass of readily fusible material which is adapted to receivev heat from said heating conductor and fuse and release its hold ori said circuit interrupting conductor, and means responsive to the fusing of said material to withdraw said circuit interrupting conductor from said block, said block having a` large heat absorbing capacity as compared with the fusible material.

'7. In a thermal circuit protector, a relatively massive infusible heat absorbing block, a heatconductor having one end thermally connected with said block, a circuit interrupting conductor electrically connected in series with said heating conductor and thermally connected with said block by a relatively small mass of readily fusible material which is adapted to receive heat from said heating conductor and fuse and release its hold on said circuit interrupting conductor, means responsive to the fusing of said material to withdraw said circuit interrupting conductor from said block, and means independent of the aforesaid elements for supporting said block.

8. In a thermal circuit protector, a heat absorbing block, a heating conductor thermally connected with said block, a flexible conductor having a reexed end thermally connected with said block and electrically connected in series with said heating conductor by a mass of readily fusible material that is adapted to receive heat from said heating conductor and fuse and release its hold on said flexible conductor, and a tension spring engaged With the reexed end of said ilexible conductor to move it in a circuit opening direction upon the fusing of said material.

9, In a thermal circuit protector, a heat absorbing block. a heating conductor thermally connected with said block, a flexible conductor having a reilexed end thermally connected with said block and electrically connected with said heating conductor by a mass of readily fusible material that is adapted to receive heat from said heating conductor and fuse and release its hold on said flexible conductor, and va, tension spring engaged with the reexed end of said flexible conductor to move it in a circuit opening direction upon the fusing 'of said material, said heating conductor comprising a fusible link.

10. In a thermal circuit sorbing block having a hole through it, a heating conductor having one end in said hole, a flexible conductor having a reiiexed end part in said hole, readily fusible material occupying said hole and connecting said conductors and block together, and a spring engaged with said reiiexed end and operative to withdraw said exible conductor from said hole upon the fusing of said material.

1l. In a thermal circuit interrupter, a massive heat absorbing block, a fusible heating conductor in heat transferring relation with said block, an infusible flexible conductor having an end connected to said block by a readily fusible material,.

andv a spring acting on theconnected end of said flexible conductor and having the major part of the length of saidexble conductor free from tension operative to withdraw said iiexible conductor from said block upon the fusing of said material, said block having a large heat absorbent capacity compared with the fusible material.

l2. In. a thermal circuit protector, a tubular enclosing casing having end terminals, a massive heat absorbing block in and engaged with a, part of said casing and comprising a partition separating the casing into two compartments, a fusible and heating conductor in one compartment having one end connected with one terminal and the other end thermally connected with said block, an arc quenching filler in said one compartment and between said block and terminaland around said heating conductor,an infusible flexible conductor having one end connected with the other terminal and the other end connected with said block and heating conductor by a readily fusible material that is adapted to receive heat from said fusible heating conductor only and fuse and release its hold on said flexible conductor, and a spring engaged with said iiexible conductor near said block and operative to move said conductor away from said block upon the fusing of said material, said block having a large heat absorbent capacity compared with the fusible material, said fusible and heating conductor being arranged to fuse and interrupt the circuit `between the terminals before saidvfusible material when traversed by a high current for a short period.

13. In a thermal circuit protector, a tubular. enclosing casing having end terminals, a heat absorbing block in and engaged with a part of said casing, a heating conductor having one end connected with one terminal and the other end thermally connected with said block, a flexible conductor having one end connected with the other terminal and the other end connected with said block and heating conductor by a readily fusible material that is adapted to receive heat from said heating conductor and fuse and release its hold on said flexible conductor, and a spring engaged with said flexible conductor near said block and operative to move said conductor away froml said block upon the fusing of said material, iarig heating conductor also comprising a fusible 14. In a. thermal circuit protector, a tubular enclosing casing having end terminals, a heat absorbing block in said casing and dividing it protector, a heat abinto two chambers, a heating conductor in one chamber having one end-connected with one terminal and its other end connected with said block, a exible conductor in the other chamber connected at one end with said other terminal and having its other end connected with saidI block, a vreadily fusible material connecting at least said flexible conductor to said block, and a spring connected with said exible conductor and operative to withdraw said exible conductor from said block upon the fusing of said material.

15. In a fusible protective device, a tubular enclosingA casing having end terminals, a conducting heat absorbing block in said casing and dividing it into twochambers, a heating conductor in one chamber connected with said block and with one terminal, a circuit interrupting conductor in the other chamber connected with one terminal and also connected with said block by a readily fusible metal in good heat receiving relation with said heating conductor and operative to be heated thereby to fuse to release its hold on said circuit interrupting conductor, and a spring in said second chamber responsive to the fusing of said material to move said circuit interrupting conductor in a circuit opening direction.

16. VIn a thermal circuit protector, an enclosing casing having an inwardly projecting part and terminals, an anchorage member on said inwardly projecting part, a circuit interrupting conductor connected between one terminal and said member and anchored to said member by a readily fusible material, spring means operative to maintain said member seated on said inwardly projecting part and to move said circuit interrupting member to circuit interrupting position in response to the fusing of said material, and a heatingconductor connected between said other terminal and said circuit interrupting conductor and operative to heat and fuse said material.

17. In a thermal circuit protector, an enclosing casing having an inwardly projecting part and terminals, an anchorage member on said inwardly projecting part, a circuit interrupting conductor connected between one terminal and said member and anchored to said member by a readily fusible material, spring means operative to maintain said member seated on said inwardly projecting part and to move said circuit interrupting member tc circuit interrupting position in response to the fusing of said material, and a heating conductor connected between said other terminal and said circuit interrupting conductor and operative to heat and fuse said material, said heating conductor also constituting a fusible link.

18. In a thermal circuit protector, an enclosing casing having an inwardly directed part and terminals, a member seated on said part, spring means holding said member on said part including a circuit interrupting conductor connected with one of said terminals, a fusible heating conductor connected with said other terminal and also with said circuit interrupting conductor by a readily fusible material adapted to fuse and release said circuit interrupting member for movement into a circuit interrupted position.

19. In a thermal circuit protector, a tubular enclosing casing having end terminals and an inwardly directed flange intermediate said terminals, a stationary heat absorbing member seated on said iiange, a circuit interrupting conductor connected with one terminal and ccnnected with said heat absorbing member by a readily fusible material, spring means associated with said member and conductor for holding said member upon said flange and for moving said cir; cuit interrupting member into a circuit opening position in response to the fusing of said material, and a heating conductor connected with the other terminal and with said circuit interrupting conductor and in thermal relation with said readily fusible material to impart heat thereto.

20. In a thermal circuit protector, an enclosing casing having terminals and an inwardly projecting part, a heat absorbing member seated upon said inwardly projecting part, and spring means urging said member against said part. Y

2/1. In a thermal circuit protector, a tubular enclosing casing having end terminals and an inwardly directed ange intermediate said terminais, circuit interrupting elements within said casing including a partition member seated on said flange, and spring means pressing said member upon said flange.

22. In a thermal circuit protector, a fuse link and a conductor having their ends connected by a readily fusible material in good thermal relation with said link and operating to fuse when sufficiently heated by said link, means separating said link and conductor in response to the fusing of said material, ay heat absorbing member in thermal relation with said material, and supporting means for said member stationary when said link and conductor separate.

23. In a thermal circuit protector,v a fuse link and a conductor having their ends connected directly by a readily fusible material, means separating said link and conductor; in response to the fusing of said material, a heat absorbing member in thermal relation with said material, and an enclosing casing for the aforesaid elements having a part engaged with and constituting a support for holding said member stationary when said link and conductor separate.

24. In a thermal circuit protector, a tubular enclosing casing having end terminals and an inwardly projecting ange, thermo-responsive circuit interrupting elementswithin said casing including a heat absorbing member in thermal relation with said elements seated upon said flange, and spring means pressing said member against said ange.

25. A circuit protective device comprising a fuse having a fusible element, and a thermal circuit interrupting device in series with said fuse having a movable member responsive to heat generated in the fuse following the blowing of the fusible element to effect the interruption of the circuit.

26. A circuit protective device comprising a fuse having a fusible element and a filler about said element, and a thermo-responsive circuit interrupting device in series with said fuse having a movable circuit interrupting member responsive to the heating of said iiller to effect interruption of the circuit through the-fuse.

27. A circuit protective device comprising a fuse having a fusible element and a filler, and a thermo-responsive circuit interrupting device having a thermo-responsive element, and means responsive to the heating of said element operative to interrupt the circuit, said thermo-responsive element being arranged in heat receiving relation with said nller and responsive to the heating thereof.

28. A circuit protective device comprising a fusible device responsive promptly to high overload tc interrupt thc circuit, a circuit interrupting device in series with said fusible device normally operative to give delayed circuit interrupfiller, a fuse link in said filler, a; movable circuit interrupting member normally restrained from movement in a circuit interrupting direction by a readily fusible material in heat transferring relation with said filler and also with said fuse link and arranged to fuse and eilect circuit interrupting movement of said circuit interrupting member in response to the heating of said fuse link and also to the heating of said illler.

30. In a circuit protective device, an enclosing casing containing a fuse link, a ller surrounding said link,.a barrier in thermal relation with said filler, a readily fusible material carried by said barrier and in good heat transferring relation therewith, a movable circuit interrupting member normally heldin circuit closed position by the solid fusible material, and means responsive to the fusing of said material to eiectmovement of said circuit interrupting member in a circuit opening direction.

3l. A circuit protective device comprising a fuse having a fuse link and a quartz sand filler f about said link adapted to carry current when ruption of the circuit through said filler.

32. A circuit protective device Lcomprising a fuse having a fusible element and a quartzsand nller adapted to carry current when unduly heated, and-a movable circuit carrying member in series with the ller responsive to the heating of said filler for interrupting the circuit therethrough.

33. In a thermal circuit protector, a fuse link, a movable circuit interrupting conductor, a low melting point material connecting said link and conductor in series and arranged in good heat transferring relation with -said fuse link to be heated and fused thereby, a spring acting on said conductor to move it to circuit open position upon the fusing of said material, and means isolating said fuse link from the force of said spring.

34. In a thermal circuit protector, a fuse link, a conductor, a readily fusible material adherent to both said link and conductor and connecting them in series, spring means for separating said fuse link and conductor upon the fusing of said material, and means for relieving at least the major portions of said fuse link and conductor from the force of said spring.

35. In a thermal circuit protector, an enclosing casing having an internal seat, a carrier having a readily fusible material, a fuse link and an unstressed conductor connected in series and con nected together by said readily fusible material, and a spring connected through said fusible material with said carrier for holding it against said seat for relieving said fuse link from stress and arranged to separate said fuse link and conductor upon the fusing of said readily fusible material. 

